The phosphatidylinositol-protein-kinase-C (PI-PKC) system is a ubiquitous second messenger system in the central nervous system. However, in contrast to the depth at which it is understood at the biochemical and molecular biological levels, there is still a paucity of information regarding its neurophysiological functions at the cellular and molecular levels. Glutamate, PKC, voltage-dependent Ca2+ channels (VDCCs) and Ca2+- dependent K+ after hyperpolarizations have all been implicated in a model of the establishment of memory traces, long-term potentiation (LTP), and in epileptic and neurodegenerative phenomena. The highest concentrations of PKC are found in the hippocampus, in which both the physiological and pathological events are known to occur. The ultimate goal of this project is to understand the role of the neurotransmitter-activated PI-PKC system in the control of neuronal excitability using state-of-the-art electrophysiological techniques in several in vitro hippocampal neuron preparations: slices, tissue-culture and acute isolation. The interrelationships among glutamate, PKC, VDCCs and the AHP have not bee clarified. This project seeks to provide this clarification using whole- cell voltage clamp and patch clamp techniques, at two levels: the nature of the second messenger control exerted by glutamate and the regulation of VDCCs and AHP channels by PKC. Investigation of these general issues will take place by testing specific hypotheses that have been developed from past work on this project. The hypotheses are: 1) that high-voltage- activated hippocampal Ca2+ channels are regulated by the action of a complementary kinase-phosphatase system involving PKC and a protein phosphatase, 2) that glutamate depresses Ca2+ currents via PKC activation and 3) that the hippocampal AHP current is regulated by PKC at the level of the single AHP channel. These hypotheses make explicit predictions and are susceptible to clear tests with voltage- and patch-clamp methods. The outcome of these tests will provide valuable information as to the functional role of the PI-PKC system, and, since ion channels and neurotransmitters to be studied have been implicated in a variety of neurological disease states, particularly epilepsy, to the understanding of, and ability to influence, these conditions as well.